Conventionally, a method of acquiring images by performing imaging with a plurality of different tube voltages by an X-ray computed tomography (CT) apparatus is available. The method is called “dual energy CT” when two different tube voltages are used. Moreover, for dual energy CT, an applied technique has been known in which two pieces of projection data collected at two different tube voltages are separated into projection data (line-integrated data) of two basis materials specified in advance, and images (basis material images) based on the abundance ratio of the basis materials are reconstructed from each of the two separated data. In the applied technique, by performing weighting calculation processing using the two basis material images, various kinds of images such as a monochromatic X-ray image, a density image, and an effective atomic number image can be acquired.
However, various kinds of the images acquired by the above applied technology are often not images of CT value information. Therefore, conventional correction processing that has been performed using CT value information after reconstruction of an X-ray CT image is often inapplicable to the various kinds of images that are acquired by the above applied technology. That is, conventionally, there is a case when it is impossible to improve the image quality of various kinds of the images that are acquired by the above applied technology.